1. Field of the Invention
The present invention relates to a piezoelectric oscillator, more particularly, it relates to a tubular piezoelectric oscillator of the type wherein a piezoelectric oscillating element, such as a piece of quartz, is elastically supported by a torsionally displacing support element or elements within a tubular vacuum casing, and two electric leads are arranged at or adjacent to the opposite ends of the tubular casing.
2. Description of the Related Art
A conventional small piezoelectric oscillator, such as a quartz oscillator, is in the shape of a hermetically sealed tubular electric element having two parallel electric leads extending from one end of the element. The conventional tubular piezoelectric oscillator contains therein a piezoelectric oscillating element supported at one end thereof in a cantilever construction, and therefore, the oscillator is easily broken if dropped. When the conventional piezoelectric oscillator is mounted on, e.g., a printed circuit board, the two electric leads of the oscillator must be bent at a right angle and inserted in the board, so that the hermetically sealed tubular body of the oscillator can be stably affixed to the surface of the printed circuit board by a suitable adhesive. Accordingly, the mounting of the conventional small piezoelectric oscillator on a printed circuit board or other diverse electric and electronic appliances is cumbersome and costly.
The above-mentioned disadvantage of the conventional small tubular piezoelectric oscillator can be eliminated by another conventional piezoelectric oscillator disclosed in, for example, Japanese Unexamined Patent Publication No. 58-219809 and Japanese Unexamined Utility Model Publication No. 55-13462. The latter conventional piezoelectric oscillator according to, e.g., Japanese Unexamined Patent Publication No. 58-219809, has a piezoelectric oscillating element, such as a piece of quartz, supported at both ends within a tubular casing consisting of a hermetically sealed glass tube. Namely, the ends of the piece of piezoelectric oscillating element are connected to solid electric leads, respectively, via a U-shaped support spring within the tubular casing. The electric leads extend respectively and sealingly outwardly from both ends of the tubular glass casing. But, due to the construction of the latter conventional piezoelectric oscillator, a different problem arises during the manufacture of the oscillator. Namely, in the case of a small piezoelectric oscillator, the piezoelectric oscillating element preferably must be held within the tubular casing under a vacuum condition, to maintain a good electric characteristic of the oscillating element, and therefore, during the production of the oscillator, air must be exhausted from the interior of the tubular glass casing and the ends of the casing must be hermetically sealed. When the air exhausting and hermetically sealing operations are carried out under a vacuum condition, care must be taken to prevent a generation of bubbles due to a gas emitted from the glass material, and therefore, the air exhausting and hermetic sealing operations are difficult and increase the cost of producing the piezoelectric oscillator. Moreover, the electric characteristic of the oscillating element held in the interior chamber of the tubular glass casing is not always stable. Accordingly, to acquire a stable electric characteristic of the oscillating element, an inert gas, such as N.sub.2 gas and He gas, must be filled in the interior of the tubular casing of the piezoelectric oscillator, which makes it difficult to produce a high quality small piezoelectric oscillator having a small electric equivalent series resistance.
On the other hand, in the conventional piezoelectric oscillator of Japanese Unexamined Patent Publication No. 58-219809, a supporting structure for the piezoelectric oscillating element within the tubular casing of U-shaped spring is provided, to soften any impulsive or impact force due to shock and vibration applied to the piezoelectric oscillating element from outside the tubular casing, and to elastically absorb stress due to thermal expansion and contraction of the oscillating element, per se, and the tubular casing, which occur when the piezoelectric oscillator is used under an environmental condition such that a temperature surrounding the oscillator varies widely from a high to a low temperature, and vice versa. The softening and absorbing operations of the conventional supporting structure by the U-shaped spring rely on the bending motion of the spring, and thus does not fully realize the above-mentioned effect. As a result, often a required electric characteristic of a small tubular piezoelectric oscillator cannot be obtained. Accordingly, a provision of an improved means for supporting a piezoelectric oscillating element in a hermetically or airtightly sealed tubular casing is needed to enable the production of a small durable tubular piezoelectric oscillator which can be used regardless of a wide temperature change from high to low and under conditions where the oscillator may be exposed to external shock and vibration applied from outside the oscillator.